1. Field of the Invention
This invention relates to gallium nitride semiconductor devices, and more particularly to gallium nitride (GaN) Schottky diodes having improved reverse breakdown voltage and current capacity for high power applications.
2. Description of the Related Art
Diode rectifiers are one of the most widely used devices for low voltage switching, power supplies, power converters and related applications. For efficient operation it is desirable for diodes to have low on-state voltage (0.1-0.2V or lower), low reverse leakage current, high blocking voltage (20-30V), and high switching speed.
The most common diodes are p-n-junction diodes on made on a silicon (Si) substrate with impurity elements introduced to modify, in a controlled manner, the diodes's operating characteristics. In addition to silicon, p-n junction diodes can also be formed on wafers of other semiconductor materials such as gallium arsenide (GaAs) and silicon carbide (SiC). One disadvantage of p-n junction diodes is that during forward conduction the power loss in the diode can become excessive for large current flow.
Another type of diode is the Schottky barrier diodes, which are formed from a rectifying metal-to-semiconductor barrier area instead of a p-n junction. When the metal contacts the semiconductor, a barrier region is developed at the junction between the two. When properly fabricated the barrier region will minimize charge storage effects and improve the diodes switching by shortening the turn-off time. [L. P. Hunter, Physics of Semiconductor Materials, Devices, and Circuits, Semiconductor Devices, Page 1-10 (1970)]Common Schottky diodes have a lower turn-on voltage (approximately 0.5V or more depending on the semiconductor band gap) than pn-junction diodes and are more desirable in applications where the energy losses in the diodes can have a significant system impact (such as output rectifiers in switching power supplies).
The application of gallium nitride semiconductor devices for use in power conversion applications have presented new design and environmental requirements for such devices, as well as manufacturing and reliability considerations that have not been satisfied by prior art gallium nitride based devices.
Prior to the present invention, there has not been a commercially acceptable high power gallium nitride Schottky diode device.